Experimental Comparison of Single-Carrier and Digital Subcarrier Multiplexing Transmissions in a W-Band 200 Gb/s Fiber-Wireless System Considering Transmitter IQ Imbalance and Skew Mitigation

In fiber-wireless integration systems, it is valuable to investigate whether digital subcarrier multiplexing (SCM) signal is effective in improving nonlinear tolerance against photodiode (PD) saturation compared to single-carrier (SC) signal. For a fair comparison, the mitigation of linear impairments especially for IQ mixing effects become significant. In this article, we first analyze the impacts of transmitter IQ mixing effects for SC and digital SCM signals. Then, we employ the real-valued multiple-input multiple-output (MIMO) post-equalizers for the PM (polarization multiplexing)-SC system and PM-SCM system so as to mitigate transmitter IQ mixing effects. Finally, we experimentally compare the nonlinear tolerance of SC, SCM with two subcarriers (SCM-2), and SCM-4 signals using QPSK, 8QAM, and 16QAM in a W-band fiber-wireless system against the pin-photodiode (PIN-PD) saturation considering noise-limited case, optimum case and non-linear case. Subcarriers for SC, SCM-2, and SCM-4 are 25GBaud, 12.5GBaud, and 6.25GBaud respectively, with a total symbol rate of 25GBaud. Maximum line rate is 200 Gb/s with the BER satisfying the 7% HD-FEC threshold when employing the PM-16QAM. The results show that SCM signal has better nonlinear tolerance against the PIN-PD saturation than SC signals when system works in the non-linear case especially when using high-order modulation formats.